There are a couple of songs that yarg has done this with, two examples for me being Anarchy In The UK by The Sex Pistols, and Sweet Talkin' Woman by ELO.
I try to launch the song on guitar, and once the song does load it only shows a vocal chart, and no longer responds to any inputs on both my guitar and my keyboard, forcing me to alt+f4 and relaunch the game every time a song with this issue is played.
From my memory this issue has only occurred with a handful of songs I downloaded from the C3 database, and no songs from chorus have had this issue. If this is incorrrect, I will update the thread accordingly.
If there are any solutions known for songs like these or if you notice anything out of the ordinary about the song files that could be altered to fix this, please let me know!